Control circuit



C. E. ATKINS CONTROL CIRCUIT July 8, 1958 Filed June 2, 1954 FTE. N

ATTORN EYS United States CNTROL CIRCUHT Carl E. Atkins, Bloomfield, N.l., assigner to 'Kung-Sol Electric Inc., Newark, N. 3., a corporation ofBelaware Application dune 2, 1954, Serial No. 433,959

liti Claims. (Ci. 3l7--13t) The present invention relates to lightresponsive co trol circuits and more particularly although notenclusively to circuits for control of the dimming switch automobileheadlamps. The circuit of the present invention while basically thatdisclosed and claimed in my copending application, Serial No. 411,208,filed February 1.8, 1954, comprises an improvement over such circuit ina number ofimportant respects.

The present circuit like that of my said copending application comprisesin general a photo-electric tube, preferably a diode, which whensubjected to light causes inif crease in current through an electronicmulti-element tube, an oscillatory circuit coupled to the electronictube and so connected in the circuit as to be quiescent except whenlight is incident on the photocathode of the photoelectric tube and arelay control tube connected to the oscillatory circuit to receivecontrolling pulses therefrom when the photoelectric tube is subjected tolight. The relay control tube is normally conductive to hold energizedin its plate circuit a sensitive relay which upon release of itsarmature closes contacts controlling the circuit of a power relay.Positive pulses delivered by the oscillatory circuit when light of agiven intensity is incident on the photocathode of the photoelectrictube drive negative the grid of the relay control tube by virtue of theself-rectit'ying properties of the cathode grid circuit of the relaycontrol tube to cause release of the sensitive relay and consequentoperation of the dimming switch by the power relay. To prevent return tothe high beam conditions when an approaching car dirns its headiightsthe circuit includes means for increasing the sensitivity to incidentlight after release of the sensitive relay.

One feature of the present invention comprises irnproved means forinsuring rapid return of the circuit to normal conditions when the lightintensity falls below a predetermined value, such means being eiectiveeven after flooding of the photocathode with light of high intensity.The multi-electrode electronic tube which l will designate as theelectrometer tube for it functions as such has its control gridconnected to the photccathode ot' the photoelectric tube. Under no lightor low light conditions the grid and the inherent capacity associatedtherewith become negatively charged by virtue of reception of electronsfrom the cathode of the electrometer tube. Consequently, when thephotoelectric tube becomes co-nductive the current through theelectrometer tube is increased and a control voltage is delivered to theoscillatory circuit to initiate oscillation thereof. in the circuit ofthe said copending application the electrometer tube operates as acathode follower, the signal to the oscillatory circuit being taken fromthe junction of a cathode resistor with the cathode of the electrometertube. As the return to normal conditions .requires negative charging ofthe control grid of that tube the presence of the cathode resistor inits circuit introduces an element of delay when thephotoelectric tubehas passed a relatively large current due to excess light on thephotocathode thereof. ln the circuit ot the present invention e estatalPatented lIuly 8, 1958 the signal from the multi-electrode tube is takenfrom the i anode rather than from the cathode and the cathode isgrounded. This permits electrons to llow from the cathode to the griddirectly from the ground rather than through a cathode resistor,insuring thereby a. quick recovery of the circuit. Quicker recovery inthe new circuit is also obtained by a novel circuit connection to thescreen grid which takes advantage of a screen grid current to depressthe screen potential and hold it low during the period of negativecharging of the control grid following cessation of light.

Another feature of the invention comprises improved means for couplingthe electrometer tube controlled by the photoelectric tube to theoscillatory circuit which obviates critical adjustments of circuitconstants and insures more stable operation of the circuit. Thisimprovement has been effected in part by the taking of the signal fromthe anode of the electrometer tube and in part by the provision betweenthe oscillatory circuit and the electrorneter tube of phase invertingand amplifying means. The oscillatory circuit is a multi-vibratornormally prevented from oscillation by the application of positivepotential to the cathode of the iirst triode thereof, a cathode resistorbeing connected between that cathode and ground. With the phaseinverting and amplifying means in the circuit, variations in value ofthe cathode resistor of the multi-vibrator circuit as for example, as aresult of change in temperature, will not affect overall operation ofthe circuit.

A further feature of the invention comprises improved coupling betweenthe multi-vibrator circuit and the relay control tube that insuresdelivery to the relay control tube of relatively larger control pulses.In the said copending application the signal to the control grid of therelay control tube was taken from the anode of the first half of themulti-vibrator circuit which half includes the cathode resistor in itscircuit. In the circuit of the present invention larger control pulsesare obtained by taking the signal from the anode of the second half ofthe multivibrator circuit, the cathode of which is grounded.

Still another and important feature of the present invention is a novelcircuit arrangement whereby pulses appearing at the anode of the relaycontrol tube are utilized for increasing the bias of the control gridduring the presence of a signal.

Other features of the invention, including improved means for renderingoperation of the electrometer tube insensitive to battery voltageuctuation will become apparent as the description proceeds.

For a better understanding of the invention and of the novel featuresthereof reference may be had to the accompanying drawing of which thesingle figure is a schematic diagram of the preferred embodimentthereof.

The circuit shown in the drawing is adapted for control of the dimmingswitch of automobile headlamps. The car carried battery of say twelvevolts is indicated diagrammatically at 2, the power relay at 4 and thesensitive relay for control of the power relay at 6. The photoelectrictube 8 is positioned for reception by the photocathode oi' light fromapproaching cars.v The anode of tube 8 is grounded and its photocathodeis connected to the control grid of a tetrode itl. Tube 1G, theelectrometer tube, may be a 6AK6 but preferably is one speciicallydesigned to reduce leakage between terminals of electrodes which are atdifferent potentials. A tube of this general type is illustrated in Fig.4 of my copending application Serial No.1326,809, led December l0, 1952,Patent No. 2,730,629, wherein is shown a triode, the control grid ofwhich is brought out to a separate terminal. In tube lt), as in the tubeof the said application, the control grid is brought out to a separateterminal as indicated diagrammatically in the drawing by the lbracketl2. The cathode of the electrorneter tube is grounded. The anode of thattube is connected through a dropping resistor iid to a line i6 which isconnected through a filter comprising a resistor and loy-pass capacitori9 to aline Ztl of regulated potential, preferably about eight volts.The potential of line Ztl is regulated by connection to the low voltageside of a ballast lamp 22 connected in series with an adjustableresistor across the battery 7.. Line 2l) through a resistor Z5 suppliesthe current for the cathode heater or" tube itl. m e screen gridcircuit, as hereinafter described, is ccl.....ected to the line i6 ofregulated and filtered voltage. Even with substantially regulatedvoltage thus applied to cathode, screen grid and anode of the tube someundesired change of anode potential may occur with change in bat-- teryvoltage because of incomplete .compensation for the change in cathodeemission. To avoid such undesired changes in anode potential, a seconddropping resistor 26 of relatively high ohmage, is provided between theanode and the positive side of battery Z. By proper selection of themagnitude of this resistor, which thus introduces a potential correctiondirect from the source, substantially complete stability of the circuitwith change in battery voltage is insured.

The screen grid of the electrometer tube is connected through twoseries-connected resistors 27 and 26 to the line 16 and the junction ofresistors 27 and 2d is connected through an adjustable resistor 3l)comprising the hc-ld control of the circuit and a resistor 32 to ground,A capacitor 34, the purpose of which will become apparent as thedescription proceeds, is connected between the screen grid of theelectrometer tube and ground. To provide increase in sensitivity afterdimming of the headlamps, the junction of resistors 27 and 23 isconnected through an adjusable resistor 36 to the front contactassociated with the grounded armature 38 of relay 6. Adjustment ofresistor 36 controls the light level at which the dimming switch will beoperated and adjustment of resistor 30 controls the light level at whichhigh beam conditions will be restored.

Before describing the remainder of the circuit the operation of theelcctrorneter tube will tirst be described. Under no light conditionsthe tube will pass a relatively small current. Electrons from thecathode will pass to the control grid and negatively charge that gridand the inherent capacity associated therewith. The potential on thescreen grid will be positive and at some value less than eight volts byvirtue of the potential drop across resistor 2S. The potential dropacross resistor 27 will be substantially negligible. The potential atthe anode of the tube will be roughly two volts if the value of resistori4- is high, say 4.7 meg. When light falls on the photocathode of thetube 8 electrons from the control grid will leak off through the tube Sreducing the negative potential of the grid and causing increasedcurrent through the electrometer tube. The potential of the auode willthus decrease to say one-half volt due to conduction through the tubeand the consequent increase in potential drop across resistors ld and26. lf the intensity of the light has high the grid will tatiesubstantial current and this screen current due to the potential dropacross resistor 27 lowers the potential of the screen and of theungrounded side of the capacitor 3a'. When the light is suddenly removefrom the photocathode the screen grid will not return to its normalpositive potential until the capacitor has regained its full charge.Thus the screen grid potential will reins-.iu for an appreciable time,permitting the control grid to regain its negative charge and duringsuch time preventing substantial conduction by the electrometer tube.

The anode of the -electrometer tube is connected to the No. l grid of aphase inverter and amplier tube lshown as a pentode. The tube di) couldbe, for example, a 6BJ6. The cathode of: tube dil is maintained atpositive potential, say about one and one-half volts, by virtue '4 of aconnection to the junction of resistors 42 and 41% connected in seriesbetween the line 16 and ground. The No. 2 or screen grid of tube itl ismaintained at the poial of line le and the No. 3 grid is tied to theanode i. ch latter is connected to line t6 through a potential t oppingresistor 46 of thc order of 68K. The anode of tube is connected throughseries-connected re` tl to ground and the junction of these reted to thecontrol grid SZ of the .first half ie triode 5d connected as amulti-vibrator. The cathode associated with this control grid ismaintained at a positive potential by virtue of a connection to thejunction of a pair of resistors 56 and 5S connected in series betweenline lr6 and ground. The anode 66 associed with 52 is connected to theline i6 through a potential dropping resistor 62 of about 15K and isconnected through capacitor 64 to the control grid 66 of the secondhaltc of the tube 5ft. The cathode associated with grid 66 is groundedand the anode 6d of the second half of the` tube is connected to line i6through a potential dropping resistor '76 of say 15K and through acapacitor 72 to control grid 52. The anode 63 is also connected througha capacitor '74 with the control grid of a relay control tube 76.

Tube '76 is a tetrode of the space charge grid type. Its cathode isgrounded and its No. l grid maintained at a positive potential by directconnection to line 20. The anode of tube '76 is connected through thewinding of relay 6 directly to the positive terminal of battery 2. Inthe absence of a signal, tube 76 is .conducting to maintain relay 6energized with its armature 3S grounding the dimming circuit of thescreen grid of the electrometer tube. When the current through tube '76decreases to a predetermined value relay 6 releases, closing the circuitof the power relay 4 through the back contact of the relay armaturePreferably to avoid damage to the relay contacts from the inductivesurge through the power relay, a resistor '78 is connected between thelow potential side of the power relay and the positive terminal of thebattery 2.

The control grid (grid No. 2) of the relay control tube 76 is providedwith a bias resistor Sil of say 3.3 meg., one end of which is groundedand the other end of which is connected to the control grid through aresistor 82 of say 150K.. Before describing the additional circuitelements associated with the control grid of the relay control tubewhich are provided to increase the bias during the presence of a signal,the overall operation of the circuit without such additional elementswill be described. When, as the result of incident light of a givenintensity the potential at the anode of the electrometer tube falls asheretofore described, current through the phase inverter and ampliertube 4t) will be reduced and consequently the potential applied to thecontrol grid 52 of the first half of the multi-vibrator will beincreased and will override the bias provided by the positive potentialon the cathode thereof. The rst half of the multi-vibrator which hadheretofore not been conducting will now conduct as the grid potentialcorresponds to that required for triggering the circuit. When the rsthalf of the multi-vibrator conducts, a negative pulse is transmittedthrough capacitor 64 to control grid 66 to reduce the current throughthat half of the tube 54. Consequently, a positive pulse is impressedupon grid 52 through condenser 72 and upon the control grid of the relaycontrol tube through capacitor 74. The potential of grid 66 then risesas capacitor 64 discharges through resistor 67. When the thresholdpotential is reached by grid 66 conduction by the second half of thetube 54 is -resumed with resultant application of a negative pulse togrid 52 to block conduction by that half of the tube. If light is stillincident on the photocathode the cycle repeats and the vibratorcontinues to transmit positive pulses to the control grid of the relaycontrol tube.

When positive pulses are impressed on'the control grid `of the relaycontrol tube, as above described,7the`cur-rentv through the tube is rstmomentarily increased and elec` trons flow to the grid to charge thecapacitor 74. As grid resistor 80 is large, these electrons cannot leakoff rapidly and hence tend to drive the grid negative, thus lowering thegrid potential and correspondingly reducing the current through therelay 6, finally causing release of the relay and energization of thepower relay 4. When the relay 6 releases the circuit through resistor 36is opened increasing the potential of the screen grid of theelectrometer tube and thereby increasing the sensitivity of the circuitto insure that high beam conditions will not be restored until theintensity of the incident light drops to a predetermined value.

The means now to be described insure that the grid bias of the relaycontrol tube will be increased during the presence of a signal. Thejunction of resistors 80 and 82 is connected through a diode 84, shownas a crystal diode, and a capacitor 86 to the anode of the relay controltube 76, the anode of the diode being connected to the junction of theresistors. A resistor 88 of say 330K is connected between the cathode ofthe diode and ground and a capacitor 90 of say .005 microfarad isconnected across bias resistor Si). When signals are impressed upon thecontrol grid of the relay control tube negative voltage Li' pulses willappear at the anode 4of the tube. These negative pulses are appliedthrough the capacit-or 86 to the cathode of the diode S4. The potentialat the anode of the diode will thus be ldriven to the lowest potentialoccurring during each such pulse .and capacitor 90 will be charged tosuch low potential. Thus during the presence of signals additionalnegative potential is automatically applied to the control grid of theoutput tube. When the signals cease, discharge of capacitor 90 throughre sistor 80 restores normal grid bias. The purpose of resistor 52 is toprevent application of the signals from the oscillator directly to thediode S4.

The invention has now been described with reference to a singleembodiment thereof and with specific reference to the control of thedimming switch of automobile headlamps. lt will be apparent, however,that the invention in its broadest aspects is not limited to suchspeciiic application. Obviously also, although certain numerical valuesfor the various constants of the circuit have been suggested theinvention is not limited to such selected constants and various changescould be made in parts of the circuit without departing from the spiritof the invention or the scope of the accompanying claims. For example,although the hold control has been shown as being in the screen circuitof the electrorneter tube adjustment for this purpose could be providedat the control grid of the rst half of the multivibrator circuit ifdesired. Also, although the diode in the grid bias circuit of the relaycontrol tube has been indicated as of the crystal type, an electronictube could Other modifications will occur be substituted therefor. tothose skilled in the art.

The following is claimed:

l. A light responsive circuit comprising in combination a photoelectrictube having a photocathode, an electronic tube having a groundedcathode, a control grid connected to said photocathode, a screen gri-dand an anode, a low voltage source of energizing potential connected tosaid anode through a dropping resistor, output means adapted to beactuated in response to a predetermined decrease in anode potentialresulting from increase in control grid potential consequent toincidence of light on said photocathode and circuit means connected tosaid screen grid for providing a -positive potential on said screen gridwhich decreases with increase in conduction of said tube, said lastmentioned circuit means including means for delaying return to normal ofthe screen grid potential during decrease in control grid potentialconsequent to cessation of light on said photocathode.

amarsi 2. The circuit according to claim l wherein said circuitconnected to said screen grid comprises a potential divider connectedacross said source, a dropping resistor interconnected between a pointon said potential divider and said screen grid and a capacitor connectedbetween said screen grid and ground, said capacitor providing said delaymeans.

3. The circuit according to claim l wherein said circuit connected tosaid screen grid includes means for adjusting the sensitivity of thecircuit to incidence of light on said photocathode.

4. A light responsive circuit comprising in combination a photoelectrictube having a photocathode, an electronic tube having a groundedcathode, a control grid connected to said photocathode, a screen gridand an anode, a low voltage source of energizing potential connected tosaid anode through a dropping resistor, potential dividing means and adropping resistor coupling said screen grid to said source, a capacitorconnected between said screen grid and ground, a normally energizedoutput electronic tube, an oscillatory circuit, biasing means normallypreventing oscillation of said oscillatory circuit, means responsive todecrease in anode potential of said iirst mentioned electronic tuberesulting from conduction by said photoelectric tube .under the iniuenceof light for overriding said biasing means, and means responsive tooscillation of said oscillatory circuit for reducing the current throughsaid output tube.

5. The circuit according to claim 4 wherein said oscillatory circuitcomprises a first and second triode connected as a multi-vibrator, thecathode of the second triode being grounded and the cathode of the irsttriode being connected to a point of positive potential providing thebiasing means normally preventing oscillation, phase inverting meanscoupling the anode of said first mentioned tube with the control grid ofthe lrst triode, and means for impressing pulses appearing at the anodeot the second triode when the multi-vibrator is oscillating upon saidout put tube.

6. In a control circuit, the combination comprising a normally energizedoutput tube having a cathode, at least one grid and an anode, a resistorof high resistance interconnecting said grid and cathode, amultivibrator adapted when oscillating to produce control pulses,biasing means normally preventing oscillation of said multivibrator, acapacitor connected between said multi-vibrator and said grid totransmit positive pulses to said grid when the multivibrator isoscillating, photoelectric means for overriding said biasing means tocause oscillation of said multivibrator when light of predeterminedintensity is incident on the photosensitive element of saidphotoelectric means, said grid when pulsed being driven negative bynegative charging of said capacitor from said cathode with consequentreduction of current through said tube, and circuit means connected tothe anode and responsive to pulsation of potential thereat forincreasing the bias on said grid when said grid is pulsed.

7. In a condition responsive circuit, a low voltage source of energizingpotential, an asymmetrical multivibrator circuit energized from saidsource and adapted, when oscillating, to yield positive voltage pulses,condition responsive means for controlling oscillation of saidmultivibrator circuit, a space charge grid tetrode coupled to saidsource and having a control grid connected to receive positive pulsesfrom said multivibrator circuit when said multivibrator circuit isoscillating, and means, including a rectifier and lilter connected inseries across said tetrode, for augmenting the negative potentialappearing between pulses at said grid.

8. The circuit according to claim 7, including a resistor connectedbetween said grid and the junction of said rectilier and lter to preventapplication of pulses from said multivibrator circuit to said rectifier.

9. The circuit according to claim 7 wherein said condition responsivemeans includes an electronic tube having a grounded cathode, a cathodeheater, a control grid the potential of which is responsive to thecondition, a screen grid and an anode and wherein means are provided forsupplying substantially regulated voltage from said source across saidheater and through dropping resistors `to said screen grid and anode,and means for increasing the stability of anode potential toiiuctuations in voltage of said source comprising a dropping resistorconnected between said source and said anode to compensate for changesin cathode emission with change in regulated voltage.

10. A light responsive circuit comprising in combination a photoelcctrietube having a photocathode, an electronic tube having a control gridconnected to said photocathode, a cathode, a screen grid and anode, alow voltage source of energizing potential and a dropping resistorconnected in a series circuit with said anode and cathode, output meansadapted to be actuated in response to a predetermined decrease in anodepotential resulting from increase in control grid potential consequentto incidence of light on said photocathode and circuit means connectedto said` screen grid for providing a positive potenF tial onsaid screengrid which decreases with increase in conduction of said tube, said lastmentioned circuit means including a capacitor for delaying return tonormal of the screen grid potential dur-ing decrease in control grid pertential Vconsequent to cessation of light on said photocathode.

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